[!142] change const to constexpr for constant values used as template parameters

Merge branch 'issue/intel_const_constexpr' into 'master'

ref:core/dune-geometry\>

### Summary

Solve an intel-compiler related error, by replacing const by constexpr for
template parameter variables.

See merge request [core/dune-geometry!142]

  [core/dune-geometry!142]: gitlab.dune-project.org/core/dune-geometry/merge_requests/142